1954 G80 Rear Brake Problem

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
Member
Posts: 92
Joined: Sat Nov 26, 2005 10:47 pm
Location: WEST MIDLANDS UK

Re: 1954 G80 Rear Brake Problem

Postby Winkie » Sat Oct 13, 2018 8:19 pm

It is clear that the expanding ends of the shoes are twisting outwards as the cam is operated. My understanding is that the fixed end of the shoes should be snug on the pivot pin, I.e. they should not be able to twist outwards to any extent. This inability to twist effectively prevents the expanding end from sliding off the cam. So I think you need to check how snug the shoes are on the pivot. Too much side play or the ability to twist significantly on the pivot may well be the problem. A bit of filing may solve the problem if the shoes do not rest smoothly and tightly on the pivot.

Member
Posts: 19
Joined: Thu Feb 08, 2018 10:27 am
Location: LEICESTERSHIRE UK

Re: 1954 G80 Rear Brake Problem

Postby mrpjhancock » Sat Oct 13, 2018 8:23 pm

Its the one that came with the bike.

Committee
User avatar
Posts: 2004
Joined: Mon Jan 01, 1990 12:00 am
Location: HAMPSHIRE UK

Re: 1954 G80 Rear Brake Problem

Postby ajscomboman » Sun Oct 14, 2018 8:29 am

mrpjhancock wrote:Iv tried the spring thing with no luck . . . . I was at the AMOC parts shop today and tried exchanging my brake shoes for some new ones. Unfortunately my shoes werent good enough to exchange. Apparently they need to be in perfect condition!
So Im stuck with the ones I have
I have attached a photo of the brake drum its self. looks like its the hardened pads that are coming into contact


I'm intrigued, please expand more on the condition of the shoes and reason for refusal, also can you post some pictures of the shoes please.

Member
Posts: 19
Joined: Thu Feb 08, 2018 10:27 am
Location: LEICESTERSHIRE UK

Re: 1954 G80 Rear Brake Problem

Postby mrpjhancock » Sun Oct 14, 2018 9:38 am

It was explained to me that the reason refusing exchange is the fact that the machining for the hardened pads has broken out the casting.
You do not have the required permissions to view the files attached to this post.

Member
Posts: 19
Joined: Thu Feb 08, 2018 10:27 am
Location: LEICESTERSHIRE UK

Re: 1954 G80 Rear Brake Problem

Postby mrpjhancock » Sun Oct 14, 2018 9:41 am

Does anyone have a set of old brake shoes they want to sell . . . . . doesnt matter if they are worn out . . . . I would use them to exchange for recon ones .. .

Member
Posts: 901
Joined: Mon Mar 24, 2014 5:44 pm
Location: Aberdeenshire

Re: 1954 G80 Rear Brake Problem

Postby Mick D » Sun Oct 14, 2018 10:24 am

Hi

Your shoes are machined in the same manner as mine - I believe this is as per design, I think someone at AMOC Spares has made a mistake.

Why not try putting a thin shim between the brake plate and shoes at the pivot pin? this should reduce the tendency for the shoes to migrate.

Regards Mick

Committee
User avatar
Posts: 2004
Joined: Mon Jan 01, 1990 12:00 am
Location: HAMPSHIRE UK

Re: 1954 G80 Rear Brake Problem

Postby ajscomboman » Sun Oct 14, 2018 10:52 am

mrpjhancock wrote:It was explained to me that the reason refusing exchange is the fact that the machining for the hardened pads has broken out the casting.


I'll take up the case, there appears to be no reason for the refusal other than the pin end. That in itself will have no detrimental effect on the shoe and won't be any problem re-lining them.

Member
Posts: 5537
Joined: Wed Sep 01, 2004 12:00 am
Location: WEST SUSSEX UK

Re: 1954 G80 Rear Brake Problem

Postby SPRIDDLER » Sun Oct 14, 2018 11:15 am

Did you have this problem with the previous cam and bought the replacement to try to cure the rubbing issue?
Before (and after operating the brake) your cam isn't covering (acting upon) the whole face of the hardened mushroom but only on the lower part. Could that be the reason why the cam is tending to lift/twist the shoe(s)? It seems that the cam isn't tall enough.
Here's my front brake and you can see that when at rest the cam covers all the face of the hardened mushroom. Could you try raising the cam by putting a washer under it and still have enough shaft exposed to fit the outer operating arm (perhaps needing a spacer collar on the outside to prevent it locking up)?

100_1399 (640x480).jpg


100_1396 (640x480).jpg
You do not have the required permissions to view the files attached to this post.
I poke badgers with spoons.

Member
Posts: 19
Joined: Thu Feb 08, 2018 10:27 am
Location: LEICESTERSHIRE UK

Re: 1954 G80 Rear Brake Problem

Postby mrpjhancock » Sun Oct 14, 2018 11:46 am

Yes my intention was to replace the cam, springs and shoes. I thought perhaps because there was some play in the cam shaft through the back plate it was twisting the cam movement and lifting the shoes. The cam is definitely the correct one as its identical to the old one (minus the worn shaft of course)

Member
User avatar
Posts: 479
Joined: Tue Mar 15, 2016 8:51 pm
Location: Bedfordshire, UK

Re: 1954 G80 Rear Brake Problem

Postby Pharisee » Sun Oct 14, 2018 12:39 pm

mrpjhancock wrote:It was explained to me that the reason refusing exchange is the fact that the machining for the hardened pads has broken out the casting.


Those shoes look identical to the ones I took to AMC Classic Spares and exchanged for a relined set with no problem at all.

PreviousNext

Return to G80 / Model 18

Who is online

Users browsing this forum: No registered users and 9 guests